The invention relates to a method, and to an arrangement for the application of said method, for the moistening of an endless web by a vaporized liquid, said web moving in a processing device.
A uniform quality is often required in a web, both in its longitudinal direction and transverse direction. It is especially important in the case of a paper web used in printing machines that a desired property, for instance glazing, thickness, density, the shrinking or the elongation property, be the same at different locations of the web. These properties are generated in the web in finishing processes thereof, for instance by calendering a moistened web. Consequently the local moisture content should not exceed a certain maximum value.
The U.S. Pat. No. 3,838,000 discloses a method for a web moistening prior to guiding the web into a calender. The average moisture generated in the web is rather low, in order not to exceed the maximum value locally. As a result, the desired property generated by this method varies considerably at different locations of the web. This property in the transverse direction of the web, for instance, is dependent on the distribution of the moistening substance taken by the web and on the calendering effect in this direction.
Attempts have been made to eliminate the variation of the desired property by arranging, in connection with the calender and in the transverse web direction, a moistening device which is divided into separate sections in said direction. The moisture of the web is increased by this moistening device. The device is located outside a web pocket, which is formed by the web guided around a so-called fly roll located at the side of the calender. A problem exists, however, in that there is no correlation between the desired property and the flow of the moistening substance supplied from a section. This means that the flow supplied from the section cannot compensate for the variations of this property taken by a web area affected by this section. Moreover, different sections operate mutually independently, whereby said property can by sections differ in the transverse direction of the web. Furthermore, a rather large portion of the moistening substance, supplied from outside the web pocket, will not at all contact the web but is directed to the environment.
Rather complicated devices located in a web pocket are presented in British Patent Specification No. 1,101,767 and German Patent Specification No. 328,786. The former device is a web deflecting bar in a calender stack, whereas the latter one is not suited for a use in a vertical calender.